The present invention relates to a booster for amplifying or magnifying force applied on an operation mechanism before the force is transferred to a succeeding mechanism, more specifically, to a booster which boosts the force particularly by utilizing a liquid pressure introduced from outside.
As can be seen often requirement for increasing braking force without increasing the stroke of various operation mechanisms such as a brake pedal caused development of many types of the booster. In all of these booster devices, the shifting amount of the input member for delivering the operation force to the booster was almost equal to the shifting amount of a power piston actuated by the liquid pressure, which means these boosters are so designed such that the power piston is shifted by the entirely identical amount to that of the input member.
It follows as a logical consequence that the stroke of the input member (hereinafter called input stroke) is always equal to or larger than the stroke of the output member (hereinafter called output stroke) and that the relationship between the operation force and the stroke (hereinafter called stroke characteristic) is also definitely determined, leaving the magnifying power or ratio alone to selection or option.
It is, on the other hand, required in brake systems or others to increase the output stroke and the output of the booster without increasing the stroke and the operation force of the operation mechanism. Especially in the vehicle brakes, due to the extremely great desire for safe and easy operation, it is absolutely necessary to minimize the stroke and depressing force of brake pedalling and to improve the brake feeling, or agreeableness of brake pedalling. It is impossible, however, to fully comply with this high degree requirement as to the conventional boosters, because of the identity of the stroke amount in the input member and in the power piston, and of the inevitable definite determination of the stroke characteristic. One of the coinventors of this invention succeeded earlier in developing a booster, wherein the relationship between the shifting amount of the input member and that of the power piston, which had been deemed as absolutely identical, can be made variable at will, which is now pending as a patent application with TOKU-GAN-SHO-52 (1977)-92360, filed with the Japanese Patent Office. This invention is a further improvement of the above-mentioned invention.